The invention relates generally to energy storage in batteries, and in particular, to a system and method for storing a part of the dynamic braking energy in hybrid vehicle including, but not limited to, locomotive and off highway vehicle batteries and then using this energy during motoring to save fuel.
Hybrid locomotives and off highway vehicles operate by storing a part of the dynamic braking energy in batteries and then using this energy during motoring to save fuel. Maximum utilization of the batteries enhances the fuel savings. The batteries can be controlled at higher power/current levels to provide better fuel saving initially; but repetitive cycling of the battery at these high power/current levels leads to higher degradation resulting in lower fuel savings over the life of the battery.
Batteries in hybrid locomotives and off highway vehicles have traditionally been controlled at a constant power/current limit based on operational and safety limits. The benefits from a hybrid can be maximized however only if the batteries are charged at maximum possible charge power/current. Further, if controlled at a constant charge power/current throughout a mission, the batteries are charged at higher rates for events where they could have been charged at lower rates. This results in higher degradation in the batteries thereby reducing their operating life.
One known technique for addressing the foregoing problems includes using two different types of energy storage devices with different characteristics. One of the devices is of high energy capacity but low power rating; while the other device is a low energy capacity battery with a high power rating. Small excursions are resolved by the high power energy storage device(s); while the bigger excursions are resolved by the high energy device(s). These high power energy storage devices generally comprise ultracapacitors or high power batteries; while the high energy devices generally comprise large capacity batteries. Use of two different types of energy storage devices undesirable adds complexity and cost to the system
Accordingly, there exists a need for a battery control scheme that allows battery charging at higher rates only during cycles where excess braking power is available. It would be advantageous if the battery control scheme employed only the present state of charge and excursion during a mission to compute the power/current control limits without any reliance on prior knowledge of drive cycles. It would be further advantageous if the battery control scheme could be uniformly applied to all locomotives running on different missions while achieving fuel saving over both a mission and lifetime.